The present invention relates to an ultrasonic motor that generates a driving force utilizing the piezo-electric action or the electrostrictive action of a piezo electric element or an electrostrictive element. More specifically, the invention relates to an ultrasonic motor utilizing standingwaves and to an analog-type electronic timepiece using the ultrasonic motor.
Two types of the ultrasonic motor are conventionally known. One is a standing-wave type motor which employs a Langevin oscillator as a driving source. Such type of motor is disclosed in U.S. Pat. No. 4,019,073. The other is a travelling-wave type motor employing travelling-wave generated on a stator for driving a rotor provided on the stator.
Such travelling-wave motor is disclosed in U.S. Pat. No. 4,513,219 to Katsuma et al., U.S. Pat. No. 4,562,374 to Sashida and European Pat. Appl. Pub. No. 169297 of Tokushima. Katsuma et al. and Sashida disclosed the travelling-wave motor employing a ring type of a piezo-electric member. This type of travelling-wave motor essentially consists of an annular vibration member and a moving member provided thereon. The principle of a conventional wave-type ultrasonic motor is shown in graphic form in FIG. 2. The vibration member has an annular piezo-electric element thereon. The vibration member is fixed to a base through a support mechanism. On the annular type piezoelectric element, a gap portion with the length of half of the arc of an electrode is provided between two electrode groups. The travelling-wave is propagated by applying and AC signal having a phase difference of 90.degree. to the two groups.
A pressure-regulating mechanism is provided on the central shaft for making a suitable contact pressure between the vibration member and the moving member to efficiently conduct the travelling-wave component to the moving member. The vibration member is supported and fixed on two circular protrusions formed on a base. The disk-shaped piezo-electric element consists of a plurality of segments interposed in such a manner that the piezo-electric element slips by a half pitch of the arc length, the piezo-electric element having an even number of electrodes in the circumferential direction in such a manner that each electrode has the same arc length.
Other conventional structures have been disclosed in, for example, Japanese Patent Laid-Open Nos. 148682/1983, 183981/1985, 207466/1985, 207469/1985 and "Ultrasonic Motor Utilizing Standing Waves of Bent Ring", Treatise of the Japanese Association of Acoustics, Tomikawa et at., Yamagata University, March, 1988.
A ring shaped vibration member has plural protuberances. A piezo-electric element is adhered to other side of the plane of the protuberances. When a high frequency voltage is applied to the piezo-electric element, the vibration member vibrates such a condition that the node of the vibration is brought to the bottom of the protuberances of the vibration member. Consequently, one of two tips of a protuberance rises higher than the other tip.
A moving member contacts to the protuberances of the vibration member in a suitable contact pressure. The vibration member deforms to rotate the moving member. This type of ultrasonic motor can rotate the moving member to the only one direction.
In the case of the travelling-wave type ultrasonic motor shown in FIG. 2 based on the above-mentioned ultrasonic motor structure, two high frequency voltages of dissimilar phases are necessary to generate progressive waves in the vibration member 1. For this purpose, therefore, there are required two booster circuits and two drive circuits making it difficult to realize the device in small size which must also include control circuits. Further, since the vibration member always comes in contact with the moving member 6 at wave front portions having the greatest vertical amplitude component, the device is readily affected by a change in the pressing force between the vibration member 1 and the moving member 6.
Further, in the case of the standing-wave type ultrasonic motor shown in FIG. 3, there is provided an advantage in that support is obtained at nodal portions of the standing-waves generated in the vibration member 1 and the piezo-electric element 2. However, the motion is obtained in one direction only. Even in the case of the ring-type vibration member 1 shown in FIG. 3, the drive force is not obtained in both the forward direction and the reverse direction.
Japanese Patent Laid-Open Nos. 183981/1985, 207466/1985 and 207469/1985 disclose standing-wave type ultrasonic motors without, however, clarifying the positions of protuberances 1a that are provided at the contacting portions of the vibration member 1 and the moving member 6. Moreover, stable motor characteristics are not obtained and the driving force is not obtained in both the forward and reverse directions.
FIG. 20 is a vertical sectional view illustrating a conventional analog-type electronic timepiece.
A stator 53 is placed on the upper surface of a main plate 40, and a coil core 52 in contact with the upper surface of the stator 53 is fastened thereto by a screw. A coil wire 51a is wound on the coil core 52 and is wired to a drive control circuit that is not shown.
A rotor 54 is rotatably incorporated in a rotor hole 53a of the stator 53, and rotation of the rotor 54 is transmitted to a fifth wheel 55, to a fourth wheel 44, to a third wheel 43, to a minute wheel 42, to another minute wheel that is not shown, and to an hour wheel 45.
When a predetermined voltage is applied to the coil wire 51a at a predetermined cycle, the rotor 54 is rotated by the magnetic force of the stator 53, such that an hour hand 32 attached to the hour wheel 45 indicates the hours, a minute hand 33 attached to the minute wheel indicates the minutes, and a second hand 34 attached to the fourth wheel indicates the seconds.